45 lines
1.3 KiB
Go
45 lines
1.3 KiB
Go
// Copyright 2012 Aaron Jacobs. All Rights Reserved.
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// Author: aaronjjacobs@gmail.com (Aaron Jacobs)
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package siv
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import (
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"log"
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"../common"
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)
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// The xorend operator of RFC 5297.
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//
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// Given strings A and B with len(A) >= len(B), let D be len(A) - len(B). Write
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// A[:D] followed by xor(A[D:], B) into dst. In other words, xor B over the
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// rightmost end of A and write the result into dst.
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func xorend(dst, a, b []byte) {
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aLen := len(a)
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bLen := len(b)
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dstLen := len(dst)
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if dstLen < aLen || aLen < bLen {
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log.Panicf("Bad buffer lengths: %d, %d, %d", dstLen, aLen, bLen)
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}
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// Copy the left part.
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difference := aLen - bLen
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copy(dst, a[:difference])
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// XOR in the right part.
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common.Xor(dst[difference:difference+bLen], a[difference:], b)
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}
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